System dynamics modelling (SDM) was used and process researched as a case to investigate its utility as a systems?based evaluation (SBE) approach. A system dynamics (SD) model was developed to evaluate the potential requirements and implications on the health systems of the ambitious antiretroviral therapy (ART) scale?up strategy in Lusaka, Zambia. Research on SDM for strategic evaluation provided insights and principles for future application of SBE. The SD diagrams readily inspired new insights while practical constraints limited use of the model for action planning. Research suggests that utility of SBE begins with engaging stakeholders to share and align their views on a representation of the system and progresses to their reinterpretations of the system that they inhabit, ultimately moving towards transformative change. Evaluators must balance two purposes in managing for utility of SBE approaches: producing a defensible representation of the system(s) and facilitating transformative change appropriately with and for system stakeholders.